1. Field of the Invention
The present invention relates to an ink jet recording apparatus, and in particular to the control of the ink droplets generation in an ink jet recording apparatus which alternately separates the leading edge of the columnar ink stream ejected from the nozzle into ink droplets of large diameter and small diameter and surely charges and deflects those ink droplets independently of each other to record images.
2. Description of the Related Art
An ink jet recording apparatus whereto the present invention is applied is the ink jet recording apparatus of the type as described in U.S. Pat. No. 4,050,077 by Takahiro Yamada and Tetsuo Doi. In such an ink jet recording apparatus, ink droplets of large diameter and ink droplets of small diameter are alternately generated, and these droplets are charged and deflected according to recording signals to control the impingement of the ink droplets against the recording sheet.
In order to attain the favorable recording at all times even if the ambient temperature of the recording apparatus or the property of the ink is changed, such an ink jet recording apparatus must be provided with a device for automatically setting such a suitable excitation state of the nozzle that ink droplets of large diameter and ink droplets of small diameter are suitably generated at all times.
An example of such a device is described in U.S. Pat. No. 4,016,571 by Takahiro Yamada. In that device, the ink droplets are charged while the excitation voltage is changed. And the excitation voltage is set at such a value that ink droplets of small diameter are generated, charged and deflected to collide against a sensor. This device is advantageously simple when only the ink droplets of small diameter are used for recording in the recording apparatus to be constituted.
In this system, however, it was sometimes impossible to charge only the droplets of small diameter by the recording signals when the precision in setting the excitation voltage at an optimum value was increased. That is to say, adjacent ink droplets of large diameter were sometimes charged, causing errors in the charging amount and the flying path of the recording ink droplets. As a result, the recording quality was lowered.
Further, in a recording apparatus using ink droplets of large diameter as well as ink droplets of small diameter, ink droplets of small diameter are sometimes charged by the recording signals for charging the ink droplets of large diameter. Accordingly, ink droplets of small diameter are sometimes deflected largely, resulting in largely disturbed recording.